Hello, and welcome to another edition of Masterpiece Theater Engineering Roundtable. This time around, SparkFun engineer Joel walks us through the steps to make a nifty handheld pH sensor, which he uses to regulate his home aquaponics system.

The schematic and code for the H2O pH Probe can be found at the GitHub repository here, and the wishlist for the parts Joel uses in his project is here. As always, if you have any questions or suggestions for this or future projects let us know in the comments, and we’ll see you next time!

Very cool project. Watching the ph of a 10g aquarium isn’t super vital, but it could be for the plants or a larger system. Keep in mind that a larger aquarium (or likely a pond for edible fish) will be more chemically stable. While all of your fish seemed fine, 73 is a bit low for all of your tropical fish who prefer a temp around 78, but they seem fine so it should be alright. Are you using an under gravel filter or are you just pumping water from the tank up to the plants? If you aren’t using a UGF I would highly recommend it for your project as they pull the fish waste through the gravel and are sometimes jokingly referred to as nitrate factories. Although, a tank of that size with that number of fish should have a fairly even chemistry from the decomposing fish waste. Good luck with the project!

Cool Project!
I’m also interested in the Aquaponics water quality monitor system. Just be curious about the difference between (Atlas Scientific) pH sensor kit and the an analog ph meter for Arduino I found these days from DFRobot.
http://www.dfrobot.com/index.php?route=product/product&filter_name=ph&product_id=1025

Any accuracy difference? I would like to build a similar platform according to the github info. ~.

Not sure about the details, but I would guess the DFRobot unit is a tad bit better but harder to interface(you have to do pH calcs yourself, not terribly hard really), it uses tant caps which will have a better response over temperature variations and you can tune the interface to the probe. On the other hand I have no idea what op-amp they are using and what means they are using to create the negative rail, so it could be worse in this aspect. The atlas unit uses a pretty good op-amp for the job and has some smoothing and noise filtering built into the software. It can be susceptible to ground loops and mains hum, but so can they all. In the end most of the units are really similar, its how you interface the probe. I am go on for a long time about these things (if you check my site you will see why :). For a curve I make a couple interfaces one is I2C, and the other is basically a Leonardo with a pH front end (Native USB allows it to hook up to Tp-Link router for Wifi for example) which can be programmed however you need! Phidgets also makes a decent interface that is ORP select able :) Hope that helps you some!

My 3 Probes choices are (from cheapest to most expensive)
K1B0 Style This one is a pretty good probe but the lead to pretty short and you shouldnt leave this submerged for long periods(reference can be refilled, so it can leak).

Mid Range, durable This one is a tough and durable probe, I had pretty good experience with it, it sometimes has issues reading right after shipping leave it upright for a few minutes and it should start reading as normal.

Higher End These are generally my favorite probes, they last forever, are of a good quality and aren’t too expensive for their performance! If you plan on doing long term in situ readings this is definitely worth the extra price.

If you need more lab grade probes I highly recommend Omega as the source. Their probes are very expensive, but are extremely high quality! Omega. Hope this helps some source more appropriate probes for their needs!

These are great references. Your “higher end” does not reference the Atlas Scientific (also it is $20 less expensive). Have you found your recommendation to be better - or is your choice based on price? Ability to buy on eBay (i.e.: less expensive).

The Atlas probe AFAIK are comparable to the “higher end” I linked(except leads are shorter 1m vs 3m, may have changed), if you are patient and willing to deal with weeding out a few sources you can get these probes for less than or about $10. I am sure Atlas sourced these probes in this manor. In the end most of the probes are really the same, what does vary is the Ag alloy used in the electrodes, the molar strength of the HCL solution gel in the reading bulb, and what the salt bridge is made of (fabric or ceramic). Body material and lead length do play a role as well (dictated by application/requirements). The cheap ones use fabric and cheaper materials, and the molar strength is often too high erroding the reading electrode prematurely, the higher quality probes will use ceramic salt bridges and will have much tighter specs. I had one probe last just over 3 years in my Aeroponics reservoir. Every water change I took it out cleaned with soft toothbrush re calibrated and put it back in:) If you track the probes calibration slope vs ideal you can tell probe condition.

The green PCB is one I had made just for this project. It may become a product in time, however, now that Atlas Scientific includes a PCB with headers attached to the BNC connector that comes with the kit, it probably won’t go beyond being a prototype. We’ll see if there’s any demand for such a breakout. Thanks for watching!

This what I assumed after a few unsuccessful searches but it was worth asking. Thanks for the reply Joel! Much appreciated!!

Will we be seeing updates on the aquaponics setup you had in the video? Or if and when you go on a much larger scale it would presumably call for a full multitasking aquaponics controller correct?!?!? Is this something will might see from you in the future?

I am planning on finishing an Instructables detailing the build within the next day or so. I’ll post links here and on the video once it’s finished. I do have some ideas in mind for future aquaponics hacks/tools. My next task is to build a cheap time lapse camera to document the plant growth in my GB. And, of course, I want to make it so that my probes are logging the data they’re collecting at some point. I’ll be sure to share my successes and failures :)

I played around (Atlas Scientific) pH sensor kit w/ my Arduino this summer. I really appreciate the simplicity you brought to calibration and then pH reading. Great job!

The challenge I have is the pH sensor costs over $100. I want to make many to stick on each of my sensor nodes. Each sensor node is attached to a hydroponic system. My intent is to grow a lot of vegetables in my house using multiple hydroponics systems and then perhaps if all goes well, make kits for others.

Is there any thought/idea to getting a pH sensor cost to sub-$10? Why is it I can buy a “good enough” pH hand held meter for sub-$10. I know it won’t be as scientifically accurate, but that is perfectly ok.

Thanks! I feel ya on the price. These sensors are not cheap. However, the pH probe by itself is only $60 if you buy directly from Atlas Scientific. Still not sub-$10, but you can save some bucks by not buying the entire kit. I’m not sure what goes into making a pH probe, but I imagine it’s a very precise workflow. I assume that’s where the price comes in. You most certainly can by cheaper probes, but, as you said, the quality diminishes as the price goes down. You just have to find a balance and decide what’s more important: accurate readings or more probes. The cheapest method is to just use the pH drops and match the colors, but to automate that, you’re going to have to pay one way or another.

You may have just saved me a lot of trial and error. I’m currently working on a similar project. One question for you Joel: My system is outside. Do you think this setup would work as a permanent probe? I was thinking about submersing it, leaving it, taking a reading every few minutes, and having a Raspberry Pi notify me if the temp/pH get out of whack. I’m also planning to have a flow sensor to ensure the system is always circulating.

Hi, glad you enjoyed the video. As for leaving the probe in the tank, I think you’ll be fine. From what I understand, as long as the probe stays wet and never dries out, it should take accurate readings for a long time. I’ve read a few places that you’ll want to recalibrate the probe every year or so, maybe more frequently. I’m pretty positive the temperature of the water won’t affect your readings (even really cold water) as long as you’re taking that into account with your sensor like I am with this device. If your readings seem way off, make sure your probe is functioning correctly before assuming anything is wrong with your water. That’s where the calibration solutions really help. The only downside to leaving it in the tank is more opportunity for alga and other grime to grow on it. That may affect your readings, so you’ll probably need to clean it off once a month or so.

The flow sensor is a good idea. You could also use a water level sensor to make sure the water is flowing, assuming you aren’t using a constant height in fish tank (CHIFT) system. But, even then, you could measure the water fluctuations in your sump tank.

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